KSI has revealed the message he sent to Anthony Joshua after it was confirmed that the former heavyweight champion would fight Jake Paul.
Joshua and Paul are scheduled to meet in Miami, Florida on December 19.
The bout will be contested over eight three-minute rounds, with both men wearing 10-ounce gloves.
Although Joshua is the overwhelming favourite, Paul has continued to insist he is capable of producing "the biggest upset in boxing history."
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One man firmly in Joshua's corner is British YouTuber KSI.
The 32-year-old has stepped into the ring several times himself, most notably in his two fights against Jake's brother Logan.
The first meeting in 2018, which was an amateur contest, ended in a majority draw before KSI won the professional rematch by split decision the following year.
There has never been any love lost between KSI and the Paul family and he revealed that he wasted no time messaging Joshua when the fight was announced.
He said: "Now we get to see Jake Paul get knocked out, fantastic.
"I messaged AJ being like, 'brother knock this guy out'.
"I want Jake to go into that ring and realise how f**ked he really is.
"Like I think Jake will already know, but I want him to truly fear the man that's in front of him.
"I just want AJ to hit him with one stiff jab, just so Jake knows what the f**k this is."
KSI's comments come as several boxers and commentators have voiced concerns about the fight, with many questioning how Paul will remain safe in the ring.
British heavyweight Dave Allen has labelled the fight a "joke," warning it is dangerous for Paul to share the ring with someone of Joshua's size and experience.
Tony Bellew has also weighed in, calling the bout "madness" and insisting Paul is in for the "fright of his life" once Joshua lands his first punch.
Joshua is five inches taller than Paul and is widely regarded as one of the best heavyweights of his generation.
Meanwhile, Paul has impressed during his five-year professional career, but he has yet to face someone as big and experienced as Joshua.
That has led many, including KSI, to believe the fight will be short.
"Because let's be honest, if this goes eight rounds, that's a loss for AJ," KSI continued.
"I don't even care if AJ wins, that's a loss for AJ and that's a win for Jake.
"Jake has to be on the floor within those eight rounds, repeatedly.
"I want a KO, I need it, I need it."
Topics: KSI, Anthony Joshua, Jake Paul, Boxing
James Taylor